Mana Party leader Hone Harawira has written an open letter to overseas investors wanting to buy shares in New Zealand state-owned enterprises (SOEs), warning them to steer clear or be caught up in legal battles.

Parliament will today debate legislation to enact the Government's policy to sell up to 49 per cent of four state-owned energy companies; Mighty River Power, Meridian Energy, Genesis and Solid Energy.

It also plans to further reduce its shareholding in Air New Zealand.

Harawira said the plan was opposed by a majority of New Zealanders because they were concerned assets built up through the hard work of generations of New Zealanders would be sold to investors who were motivated by profit, not the public good.

"As the indigenous people of Aotearoa, Maori have been even stronger in their opposition. The Maori view is that no asset sales should proceed until Maori interests in those assets have been properly addressed."

The Maori Council has an application before the Waitangi Tribunal over water issues relating to the sales and Harawira said there was a separate case before the High Court.

"Steps are being taken to take the case to the United Nations (under the Declaration on the Rights of Indigenous Peoples) and Maori groups have pledged to take action against sales to overseas interests which impact on our sovereignty."

The High Court's ruling last month overturning the Government's decision to approve the sale of the 16 North Island Crafar farms to a Chinese company was also related, he said.

"So today I think it only proper to send a warning to overseas investors - steer clear of any share offer in the above SOEs.

"The purchase of these shares is likely to see you caught up in legal battles and direct action from citizens determined to protect their own interests, both of which will be lengthy and costly and have an adverse impact on the value of your investment."

Mana would strongly push for any shares sold to overseas investors to be returned to New Zealand hands, Harawira said.

"You have been warned."

All opposition parties and the Maori Party are expected to oppose the Government's legislation which it has a majority to pass with just one vote following support from ACT leader John Banks and United Future leader Peter Dunne.